Getting rid of OS::StrDup and OS::StrNDup which were sometimes misused.

src/platform-macos.cc

Index: src/platform-macos.cc
===================================================================
--- src/platform-macos.cc	(revision 1525)
+++ src/platform-macos.cc	(working copy)
@@ -202,28 +202,6 @@
 }
 
 
-char* OS::StrDup(const char* str) {
-  return strdup(str);
-}
-
-
-char* OS::StrNDup(const char* str, size_t n) {
-  // Stupid implementation of strndup since macos isn't born with
-  // one.
-  size_t len = strlen(str);
-  if (len <= n) {
-    return StrDup(str);
-  }
-  char* result = new char[n+1];
-  size_t i;
-  for (i = 0; i <= n; i++) {
-    result[i] = str[i];
-  }
-  result[i] = '\0';
-  return result;
-}
-
-
 // We keep the lowest and highest addresses mapped as a quick way of
 // determining that pointers are outside the heap (used mostly in assertions
 // and verification).  The estimate is conservative, ie, not all addresses in